The present invention relates to an aperture device of a radiation diagnostic apparatus capable of performing stereoscopic and monoscopic radiography or fluoroscopy and, more particularly, to an aperture device for precisely aligning a radiation area with a predetermined area.
An X-ray diagnosis apparatus having radiographic and fluoroscopic functions has been used in X-ray diagnosis of circulatory organs so as to perform angiography of cerebral, heart and abdominal areas. A conventional X-ray diagnostic apparatus is illustrated in FIG. 1. A U-shaped arm 12 is supported on a vertical support 10 to be rotatable around a horizontal axis. Horizontal, reciprocal arms 14 and 20 are mounted at two ends of the arm 12. An X-ray tube 16 and an X-ray aperture device 18 are mounted on the arm 14. An X-ray fluoroscopic image intensifier (to be referred to as an I.I hereafter) 22, a cine camera 24 and a television camera 26 are mounted on the arm 20. The arm 20 also has an X-ray film changer 28 for X-ray radiography. When a patient 32 lying on a table top 30 is positioned between the X-ray tube 16 and the film changer 28, the X-ray emitted from the X-ray tube 16 passes through the patient 32. A transmitted X-ray image is detected by the film changer 28. This radiographic or fluoroscopic position can be adjusted by reciprocal movement of the arms 14 and 20 and rotation of the arm 12.
In cardiac and coronary angiography, X-rays emitted from two focal points are used to obtain an X-ray image, thereby obtaining a stereoscopic image. Three-dimensionally branched blood vessels in a complicated structure can be rendered more distinct. In order to observe the stereoscopic transmitted image, a stereo cine camera and a stereo projector have been recently developed. As a result, static or dynamic stereoscopic observation or stereo observation by several observers in an observation room can be performed.
In stereo radiography or fluoroscopy, the X-ray radiation area is defined by the X-ray aperture device 18, as shown in FIG. 2. High-speed electron beams are supplied to two positions L and R of a rotary anode 34 of the X-ray tube 16, and conical X-ray beams 36 and 38 are emitted from these two positions. These X-ray beams 36 and 38 are defined by fixed blades 40 and 44 and moving blades 42, 46 and 48 and then irradiate the patient 32.
In this conventional X-ray diagnostic apparatus, in order to change the X-ray radiation area in the stereoscopic view, a beam component of the X-ray beam 36 at the side of the X-ray beam 38 and a beam component of the X-ray beam 38 at the side of the X-ray beam 36 are not subjected to stopping since the blades 40 and 44 are fixed in position, as shown in FIG. 3. An unnecessary X-ray component irradiating the patient 32 is represented by a hatched area in FIG. 3. When a distance SID (source to image distance) between the X-ray focal points R and L and an imaging surface 50 changes, the radiation area of the X-ray beam 36 does not match with that of the X-ray beam 38. As a result, a clear X-ray image cannot be obtained. Therefore, the radiography must be performed at the predetermined distance SID.
FIG. 4 is an enlarged view illustrating the aperture device 18 used in adjusting an area of the radiation received by the patient. Before radiation, the positions of the moving blades 42, 46 and 48 are adjusted by utilizing light rays from lamps 52 ard 54. The lamps 52 and 54 are located at positions to coincide with the X-ray focal points R and L through mirrors 56 and 58, respectively. The light rays from the lamps 52 and 54 irradiate the same area as that of X-rays from the X-ray focal points R and L. Thus, positions of the blades are adjusted such that the light rays from the lamps 52 and 54 irradiate a predetermined area prior to X-ray radiation. The adjustment of the X-ray radiation area can be performed in an over-tube system X-ray diagnostic apparatus wherein the X-ray tube 16 is located above the patient 32. However, in an under-tube system apparatus wherein the arm 12 is rotated by a half revolution thus moving the X-ray tube below the patient 32, the light rays from the lamps are shielded by the table top 30, thereby preventing pre-adjustment of the X-ray radiation area. In the under-tube system, the relatively compact X-ray tube 16 is located below the table top 30, so that the height of the table top 30 can be decreased and operability can be improved. In addition, in the under-tube system, an amount of X-ray exposure of the patient 32 can be decreased (especially, his crystalline lenses) as compared with the amount of exposure by the over-tube system. Even though the under-tube system has these advantages, it is inconvenient that the X-ray radiation area cannot be adjusted prior to X-ray radiation. Although the under-tube system prevents pre-adjustment of the radiation area, this problem can be overcome by using an I.I. When a large diameter I.I having the same size as the photographing film is incorporated in the X-ray diagnosis apparatus, it becomes large, thus making it impractical. In addition, when the lamps 52 and 54 and the mirrors 56 and 58 are also mounted in the apparatus, the apparatus becomes larger.